BRUSSELS, Jan 27 (Reuters) - NATO faces tough decisions next month about whether to pull all its troops out of Afghanistan after this year if President Hamid Karzai does not sign accords allowing them to stay, the alliance's leader said on Monday.

Anders Fogh Rasmussen repeated his warning that the 28-nation alliance would be forced to pull all its troops out of Afghanistan by year-end if it does not have a legal framework in place to keep some there.

The Afghan government and the United States have agreed the legal terms for U.S. troops to stay in Afghanistan after the end of 2014, when NATO-led forces are due to end combat operations, leaving behind a much smaller training and advisory mission.

But Karzai has said he will not sign the agreement unless certain conditions are met, and even then, not until after April elections.

"For planning reasons, we need to know soon whether we're invited or not. If we are not invited, if we don't have any legal framework, then we can't stay in Afghanistan after 2014, it is as simple as that, and it takes some time to close down our bases in Afghanistan," an unusually emotional Rasmussen told a news conference.

Rasmussen declined to say how long NATO could wait to reach an agreement and still have enough time to prepare for the new post-2014 mission. But if there is no deal, it would have to withdraw all forces and equipment by the end of this year.

"So we'll discuss it when defence ministers meet here at headquarters (in late February) and I think at that time we will have to take some tough decisions," he said.

DELAYS

NATO is negotiating a separate pact with the Afghan government to allow troops from other NATO nations to stay on beyond 2014 but says it will not finalise that agreement until the U.S. pact is signed.

The delays in agreeing legal terms have frustrated NATO military planners, who have not been able to draw up detailed plans for the post-2014 mission, nor seek firm offers of troop contributions from NATO members.

A NATO source said the February meeting was not necessarily a cut-off point for keeping NATO troops in Afghanistan beyond 2014. But NATO military planners would have to draw up plans for all options, including the possibility of a total troop pullout.

The NATO-led force currently has around 57,000 soldiers in Afghanistan, two-thirds of them from the United States. Troop numbers are expected to fall to 8,000-12,000 after 2014.

A complete foreign military withdrawal from Afghanistan could also jeopardise foreign military aid needed to finance the 350,000-strong Afghan security forces as well as development aid, Rasmussen said.

The foreign aid totals about $8 billion a year.

"I don't know how the Afghans will be able to ... pay salaries to soldiers and police if they don't get any support from the international community," he said.

Karzai's delay in signing the security agreement has angered the United States, which also opposes Kabul's plans to release scores of prisoners it regards as a security threat.

Karzai's spokesman said this month that Afghanistan has enough evidence to try only 16 of 88 prisoners that the United States considers a security threat and plans to free the rest.

Rasmussen said he would be concerned if the prisoners were released for political reasons instead of following a normal legal process.

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